This invention relates to undersea cables and more particularly to undersea cables for simultaneously transmitting power by a metallic conductor and data and control signals by optical fibers.
The improved data transmitting capabilities of optical fibers have greatly increased their use as manufacturing techniques have improved performance and reduced cost. Multi-mode and single-mode fibers readily lend themselves for inclusion in undersea cables where weight and size constraints, among others, further limit the desirability of metallic conductors.
One design disclosed in U.S. Pat. No. 4,037,923 and entitled "Optical Guides with Compressible Cellular Material" by Richard Ernest Beal has a number of optical fibers radially disposed about an axial load-bearing member. A cushioning material was interposed and a protective sheath helped prevent damage and assured that the fibers could transmit data with some measure of reliability. Derek William Stenson et al in U.S. Pat. & Trademark No. 4,038,489 provided a central tensile member and a coaxially disposed tensile sheath which interposed a number of dielectric optical waveguides. An outer sheath serves to protect the rest of the elements against corrosion. The tensile members bear the load and the tensile sheath and outer sheath protect the waveguides during the laying of the cable. Further protection from externally originating mechanical stresses is provided for by the optical cable of Ulrich Oestreich as described in U.S. Pat. and Trademark Office No. 4,076,382. A spring steel core is covered by a polyurethane layer which sandwiches a layer of optical transmission elements between successive layers of plastic and polyvinylchloride. Inner and outer armor layers fabricated from a prestretched aromatic polyamide assure the necessary protection of the data carrying elements during deployment and retrieval.
The optical fiber cable of Hiroyuki Kumamaru et al in U.S. Pat. and Trademark No. 4,097,119 has a cable including a strengthening member cushioning optical fiber reinforcing layers to avoid the problems normally associated with bending highly fused silica fibers during deployment. The cable resists breaking the optical fibers as the cable is twisted and pulled during deployment so that the fibers' data transmitting capabilities are not compromised. Gene S. Anderson in U.S. Pat. and Trademark Office No. 4,143,942 shows a further improvement over the state-of-the-art; tensile strength members, fiber optical elements and coaxial sheaths are held together by tape to facilitate being stripped back and exposing the inner elements of the cable while also functioning as a heat barrier. The U.S. Pat. and Trademark Office No. 4,169,657 by Kenneth L. Bedard entitled "Laminated Strength Members for Fiber Optic Cable" sought to increase reliability by including a coaxial prestretched strength member about an axially running optical fiber. Prestressing the strength member sought to prevent cracking or breaking of the fiber when longitudinal strains became excessive. A later design by Ulrich Oestreich disclosed in U.S. Pat. and Trademark Office No. 4,199,224 was a number of optical cables disposed in a number of chambers about a coaxial load-bearing member so that they are movable radially to protect the optical conductors from tensile, compressional and flexural stresses.
The submarine cable for optical communications designed by Richard C. Mondello in U.S. Pat. No. and Trademark Office No. 4,156,104 was specifically designed to reduce the mechanical stresses on a submarine cable which occur during laying and recovery. Particular attention was given to providing hermetic protection of the optical fibers against moisture since it was learned that the combination of moisture and stress on an optical fiber quickly leads to structural failure. In addition, this cable included an efficient d.c. path for powering a number of optical repeaters and was fabricated to be sufficiently strong to withstand the deployment stresses and years of operation at sea. An axially extending tensile load-bearing member is surrounded by a number of optical fibers embedded in an elastomeric portion. Another group of load-bearing members is radially outwardly disposed and a d.c. conducting path is formed directly over the second load-bearing members. Outwardly of this a dielectric and a vinyl jacket provides for electrical insulation and protection of the cable, respectively. Tensile loads apparently are borne by the axial and the radially outwardly disposed members; however, it is not apparent if any consideration has been given as to how these loads have been balanced between the two.
The consequent torsional strains created during deployment and retrieval may effect the structural integrity of the embedded optical fibers since their separation from the axis of the cable must necessarily magnify the torsional motions and, as a result, will magnify the compressive and tensile strains on the fibers. Furthermore, the dielectric material carried radially outwardly from the load-bearing members is more vulnerable to abrasions and punctures leading to failure of the d.c. power system. The outermost jacket, while affording some degree of protection, may be inadequate to provide a sufficient safeguard for protecting the dielectric material from breakdown.
One of the latest developments is shown in U.S. Pat. and Trademark Office No. 4,239,336. This Optical Communication Cable has information carrying fibers inside of an electrical conductor which, in turn, are carried inside of a dielectric layer and a tubular strength member. It appears that the strength member is a wire rope affair that affects the cable's weight and flexibility. These properties are critical during cable laying since experience has demonstrated that damage is likely to occur, if at all, while the cable is being deployed.
The several cable designs discussed make use of the advantages of fiber optic data transmitting cables and all have advantages and answer a long felt need to one degree or another. Most of the cables described do not provide for transmitting the electrical power along with the data transmitting optical fibers. Some locate the fibers at a distance from the cable axis and, consequently, subject the fibers to magnified strains when the cables are flexed or bent. One design that does include a d.c. power transmission capability leaves the dielectric insulation somewhat exposed to abrasions and punctures and increases the chances of shorting out the d.c. power system. The other d.c. power-fiber data cable apparently could be unduly weighty or cumbersome for some applications.
Thus, there is a continuing need in the state-of-the-art for an optical data transmitting undersea cable including its own power conductor that does not subject the data carrying optical fibers to excessive strains during deployment and retrieval, that protects the insulating dielectric layer from abrasions and punctures, that allows for the sharing of the tensile load by the load-bearing and armor layer along with the d.c. conductor and which is configured to cushion the elements during deployment.